This invention relates to household refrigerators and is more particularly concerned with a combination refrigerator, that is, a refrigerator including a freezer compartment on top and a fresh food compartment below, both of which are cooled by circulation air over a single evaporator employing a single fan to accomplish the circulation. This invention relates to an air flow system for reducing the amount of natural convection heat transfer that takes place between the area around the evaporator and the fresh food compartment when the evaporator fan is not operating.
Combination refrigerators, including a single evaporator and a single fan for circulating air from the freezer and fresh food compartments over the evaporator are well known. In the operation of such refrigerators, a major portion of the refrigerated air from the evaporator is directed into the freezer compartment while a smaller portion is directed into the fresh food compartment.
Various means have been used or proposed for providing temperature control employing a single thermostat for maintaining the two compartments within their desired operating temperature ranges. Such means of control are described in U.S. Pat. Nos. 3,320,761 and 4,229,945. Generally, thermostatic control of the evaporator is achieved by using an air temperature sensing element in the warmer fresh food compartment. The air from the evaporator is divided by appropriate structure with about 80-90 percent going to the freezer compartment from the evaporator area and about 10-20 percent to the fresh food compartment, to thus provide the desired temperature differential between the freezer and fresh food compartments.
The air flow from the evaporator area to the fresh food compartment is by a duct that receives cold air from the evaporator and discharges it into the fresh food compartment through an air flow control assembly in the fresh food compartment. The air flow control assembly may be adjusted during a particular ambient atmospheric condition, for example, 70.degree. F.; however, satisfactory temperature control may not be acheived at a higher ambient atmospheric temperature, for example, l00.degree. F., due to the unequal proportion of heat flow into the fresh food compartment. In the higher ambient temperatures, the heat flow from the ambient into the fresh food compartment is higher relative to the freezer compartment than in low ambient temperatures. This can be remedied by increasing the amount of cold air flowing into the fresh food storage compartment in higher ambients. Such changes in usage conditions may be accommodated by including a manually-operable fresh food compartment air flow adjustment such as a damper. There may also be a temperature sensing means located adjacent the cold air duct upstream of the damper that controls the operation of the compressor and evaporator. When the temperature sensed by the temperature sensing means located in the fresh food compartment reaches a pre-selected elevated temperature, there are electrical means for turning on the compressor which in turn will operate the evaporator and turn on the evaporator fan along with the compressor to increase the flow of cold air.
It has been found that when the evaporator fan is not operating there results natural convection heat transfer between the evaporator area and fresh food compartment which decreases the amount of controlled forced air flow to the fresh food compartment, thus detrimentally affecting temperature control repeatability of the refrigeration system. Such natural convection heat transfer also increases the amount of cross-ambient compensation which is undesirable. Cross-ambient compensation means that there is a temperature differential change from one ambient temperature (90.degree. F.) to another (70.degree. F.) in each of the fresh food and freezer compartments. Ideally, the less cross-ambient temperature differential the better. By this invention there is a reduction in these undesirable characteristics in a household refrigerator refrigeration system.